1. Field of the Invention
The invention relates to a technique for obtaining an amount of received light reflected from a light-irradiated area of a rotating conveyor member.
2. Description of Related Art
A known image forming apparatus performs a function of correcting positional deviation, e.g., deviation of an image forming position on a sheet. In the image forming apparatus, a pattern, which includes a plurality of marks, e.g., a registration pattern, is formed on a belt, and, while the image forming apparatus irradiates the belt with light, an optical sensor receives light reflected from the belt. The image forming apparatus determines a position of a mark on the belt based on an amount of reflected light received by the optical sensor. In particular, the image forming apparatus determines the position of the mark based on a difference between a reflectance of a surface of the belt and a reflectance of a surface of the mark and determines the difference in the reflectances. Alternatively, the image forming apparatus determines the position of the mark based on amounts of received reflected light and determines a difference between the amount of reflected light received from the surface of the belt and the amount of reflected light received from the surface of the mark. The image forming apparatus corrects the deviation of the image forming position based on the position of the mark on the belt determined from the amount of reflected light received by the optical sensor.
The surface of the belt, however, may become dirty or damaged. The dirt or damage on the surface of the belt may diffuse light reflected off the surface of the belt. This may cause a decrease in the reflectance of the surface of the belt and may prevent the image forming apparatus from determining the position of the mark. To reduce the occurrence of this problem, a known image forming apparatus irradiates a surface of a belt on which a mark is not formed with light, and the image forming apparatus adjusts a sensitivity of an optical sensor based on an amount of reflected light from the belt surface received by the optical sensor.